Different types of organism have different essential nutrients. Ascorbic acid (vitamin C) is essential, meaning it must be consumed in sufficient amounts, to humans and some other animal species, but not to all animals and not to plants, which are able to synthesize it. Nutrients may be organic or inorganic: organic compounds include most compounds containing carbon, while all other chemicals are inorganic. Inorganic nutrients include nutrients such as iron, selenium, and zinc, while organic nutrients include, among many others, energy-providing compounds and vitamins.

A classification used primarily to describe nutrient needs of animals divides nutrients into macronutrients and micronutrients. Consumed in relatively large amounts (grams or ounces), macronutrients (carbohydrates, fats, proteins, water) are used primarily to generate energy or to incorporate into tissues for growth and repair. Micronutrients are needed in smaller amounts (milligrams or micrograms); they have subtle biochemical and physiological roles in cellular processes, like vascular functions or nerve conduction. Inadequate amounts of essential nutrients, or diseases that interfere with absorption, result in a deficiency state that compromises growth, survival and reproduction. Consumer advisories for dietary nutrient intakes, such as the United States Dietary Reference Intake, are based on deficiency outcomes[clarification needed] and provide macronutrient and micronutrient guides for both lower and upper limits of intake. In many countries, macronutrients and micronutrients in significant content[clarification needed] are required by regulations to be displayed on food product labels. Nutrients in larger quantities than the body needs may have harmful effects.[1] Edible plants also contain thousands of compounds generally called phytochemicals which have unknown effects on disease or health, including a diverse class with non-nutrient status called polyphenols, which remain poorly understood as of 2017.

Plant nutrients consist of more than a dozen minerals absorbed through roots, plus carbon dioxide and oxygen absorbed or released through leaves. All organisms obtain all their nutrients from the surrounding environment.[2][3]

An essential nutrient is a nutrient required for normal physiological function that cannot be synthesized in the body – either at all or in sufficient quantities – and thus must be obtained from a dietary source.[8][9] Apart from water, which is universally required for the maintenance of homeostasis in mammals,[10] essential nutrients are indispensable for various cellular metabolic processes and maintaining tissue and organ function.[11] In the case of humans, there are nine amino acids, two fatty acids, thirteen vitamins and fifteen minerals that are considered essential nutrients.[11] In addition, there are several molecules that are considered conditionally essential nutrients since they are indispensable in certain developmental and pathological states.[11][12][13]

Minerals are the exogenouschemical elements indispensable for life. Although the four elements: carbon, hydrogen, oxygen, and nitrogen, are essential for life, they are so plentiful in food and drink that these are not considered nutrients and there are no recommended intakes for these as minerals. The need for nitrogen is addressed by requirements set for protein, which is composed of nitrogen-containing amino acids. Sulfur is essential, but again does not have a recommended intake. Instead, recommended intakes are identified for the sulfur-containing amino acids methionine and cysteine.

Conditionally essential nutrients are certain organic molecules that can normally be synthesized by an organism, but under certain conditions in insufficient quantities. In humans, such conditions include premature birth, limited nutrient intake, rapid growth, and certain disease states.[12]Choline, inositol, taurine, arginine, glutamine and nucleotides are classified as conditionally essential and are particularly important in neonatal diet and metabolism.[12]

Ethanol (C2H5OH) supplies calories. For spirits (vodka, gin, rum, etc.) a standard serving in the United States is 1.5 US fluid ounces (44 ml), which at 40%ethanol (80proof) would be 14 grams and 98 calories. At 50%alcohol, 17.5grams and 122.5calories. Wine and beer contain a similar amount of ethanol in servings of 5 US fluid ounces (150 ml) and 12 US fluid ounces (350 ml), respectively, but these beverages also contain non-ethanol calories. A 5-ounce serving of wine contains 100 to 130 calories. A 12-ounce serving of beer contains 95 to 200 calories.[citation needed] According to the U.S. Department of Agriculture, based on NHANES 2013–2014 surveys, women ages 20 and up consume on average 6.8grams of alcohol per day and men consume on average 15.5 grams per day.[22] Ignoring the non-alcohol contribution of those beverages, the average ethanol calorie contributions are 48 and 108 cal/day, respectively.[citation needed] Alcoholic beverages are considered empty calorie foods because, other than calories, they contribute no essential nutrients.[citation needed]

By definition, phytochemicals include all nutritional and non-nutritional components of edible plants.[23] Included as nutritional constituents are provitamin A carotenoids,[24] whereas those without nutrient status are diverse polyphenols, flavonoids, resveratrol, and lignans – often claimed to have antioxidant effects – that are present in numerous plant foods.[25] A number of phytochemical compounds are under preliminary research for their potential effects on human diseases and health.[23][24][25] However, the qualification for nutrient status of compounds with poorly defined properties in vivo is that they must first be defined with a Dietary Reference Intake level to enable accurate food labeling,[26] a condition not established for most phytochemicals that are claimed to be antioxidant nutrients.[27]

An inadequate amount of a nutrient is a deficiency. Deficiencies can be due to a number of causes including an inadequacy in nutrient intake, called a dietary deficiency, or any of several conditions that interfere with the utilization of a nutrient within an organism.[1] Some of the conditions that can interfere with nutrient utilization include problems with nutrient absorption, substances that cause a greater than normal need for a nutrient, conditions that cause nutrient destruction, and conditions that cause greater nutrient excretion.[1] Nutrient toxicity occurs when excess consumption of a nutrient does harm to an organism.[28]

In the United States and Canada, recommended dietary intake levels of essential nutrients are based on the minimum level that "will maintain a defined level of nutriture in an individual", a definition somewhat different from that used by the World Health Organization and Food and Agriculture Organization of a "basal requirement to indicate the level of intake needed to prevent pathologically relevant and clinically detectable signs of a dietary inadequacy".[29]

In setting human nutrient guidelines, government organizations do not necessarily agree on amounts needed to avoid deficiency or maximum amounts to avoid the risk of toxicity.[30][31][32] For example, for vitamin C, recommended intakes range from 40 mg/day in India[33] to 155 mg/day for the European Union.[34] The table below shows U.S. Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for vitamins and minerals, PRIs for the European Union (same concept as RDAs), followed by what three government organizations deem to be the safe upper intake. RDAs are set higher than EARs to cover people with higher than average needs. Adequate Intakes (AIs) are set when there is not sufficient information to establish EARs and RDAs. Governments are slow to revise information of this nature. For the U.S. values, with the exception of calcium and vitamin D, all of the data date to 1997-2004.[15]

For niacin and magnesium there appears to be a contradiction inherent in the information in the table, as the amounts recommended for daily consumption can be more than the amounts identified as the safe upper limits. For both nutrients, the ULs identify the amounts which will not increase risk of adverse effects when the nutrients are consumed as a serving of a dietary supplement. Magnesium above the UL may cause diarrhea. Niacin above the UL may cause flushing of the face and a sensation of body warmth. Each country or regional regulatory agency decides on a safety margin below when symptoms may occur, so the ULs can differ.[30][31]

EAR U.S. Estimated Average Requirements.

RDA U.S. Recommended Dietary Allowances; higher for adults than for children, and may be even higher for women who are pregnant or lactating.

AI U.S. Adequate Intake; AIs established when there is not sufficient information to set EARs and RDAs.

PRI Population Reference Intake is European Union equivalent of RDA; higher for adults than for children, and may be even higher for women who are pregnant or lactating. For Thiamin and Niacin the PRIs are expressed as amounts per MJ of calories consumed. MJ = megajoule = 239 food calories.

Upper Limit Tolerable upper intake levels.

ND ULs have not been determined.

NE EARs, PRIs or AIs have not yet been established or will not be (EU does not consider chromium an essential nutrient).

^ abDietary Reference Intakes: The Essential Guide to Nutrient Requirements, published by the Institute of Medicine's Food and Nutrition Board, currently available online at "Archived copy". Archived from the original on 2014-07-05. Retrieved 2014-07-14.CS1 maint: Archived copy as title (link)